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Pressure Pulse (pressure + pulse)

Distribution by Scientific Domains

Medical Sciences	50%
Chemistry	16%

Selected Abstracts

Respiratory units of motor production and song imitation in the zebra finch

DEVELOPMENTAL NEUROBIOLOGY, Issue 2 2002
Michele Franz
Abstract Juvenile male zebra finches (Taeniopygia guttata) learn a stereotyped song by imitating sounds from adult male tutors. Their song is composed of a series of syllables, which are separated by silent periods. How acoustic units of song are translated into respiratory and syringeal motor gestures during the song learning process is not well understood. To learn about the respiratory contribution to the imitation process, we recorded air sac pressure in 38 male zebra finches and compared the acoustic structures and air sac pressure patterns of similar syllables qualitatively and quantitatively. Acoustic syllables correspond to expiratory pressure pulses and most often (74%) entire syllables are copied using similar air sac pressure patterns. Even notes placed within different syllables are generated with similar air sac pressure patterns when only segments of syllables are copied (9%). A few of the similar syllables (17%) are generated with a modified pressure pattern, typically involving addition or deletion of an inspiration. The high similarity of pressure patterns for like syllables indicates that generation of particular sounds is constrained to a narrow range of air sac pressure conditions. Following presentation of stroboscope flashes, song was typically interrupted at the end of an expiratory pressure pulse, confirming that expirations and, therefore, syllables are the smallest unit of motor production of song. Silent periods, which separate syllables acoustically, are generated by switching from expiration to inspiration. Switching between respiratory phases, therefore, appears to play a dominant role in organizing the stereotyped motor program for song production. © 2002 Wiley Periodicals, Inc. J Neurobiol 51: 129,141, 2002 [source]

Ventricular Fibrillation Induced by Stretch Pulse: Implications for Sudden Death Due to Commotio Cordis

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 9 2006
FRANK BODE M.D.
Introduction: Nonpenetrating chest wall impact (commotio cordis) may lead to sudden cardiac death due to the acute initiation of ventricular fibrillation (VF). VF may result from sudden stretch during a vulnerable window, which is determined by repolarization inhomogeneity. Methods: We examined action potential morphologies and VF inducibility in response to sudden myocardial stretch in the left ventricle (LV). In six Langendorff perfused rabbit hearts, the LV was instrumented with a fluid-filled balloon. Increasing volume and pressure pulses were applied at different times of the cardiac cycle. Monophasic action potentials (MAPs) were recorded simultaneously from five LV epicardial sites. Inter-site dispersion of repolarization was calculated in the time and voltage domains. Results: Sudden balloon inflation induced VF when pressure pulses of 208,289 mmHg were applied within a window of 35,88 msec after MAP upstroke, a period of intrinsic increase in repolarization dispersion. During the pressure pulse, MAPs revealed an additional increase in repolarization dispersion (time domain) by 9 ± 6 msec (P < 0.01). The maximal difference in repolarization levels (voltage domain) between sites increased from 19 ± 3% to 26 ± 3% (P < 0.05). Earliest stretch-induced activation was observed near a site with early repolarization, while sites with late repolarization showed delayed activation. Conclusions: Sudden myocardial stretch can elicit VF when it occurs during a vulnerable window that is based on repolarization inhomogeneity. Stretch pulses applied during this vulnerable window can lead to nonuniform activation. Repolarization dispersion might play a crucial role in the occurrence of fatal tachyarrhythmias during commotio cordis. [source]

HIGH PRESSURE INACTIVATION OF PECTIN METHYL ESTERASE IN ORANGE JUICE USING COMBINATION TREATMENTS

JOURNAL OF FOOD BIOCHEMISTRY, Issue 6 2001
S. BASAK
ABSTRACT The contribution of several high pressure (HP) processing related factors (pressure level, 300-400 MPa; pressure cycle, 1-3, and pressure-hold time, 30,120 min) on the inactivation of pectin methyl esterase (PME) in single strength (pH 3.7 and 11.4 °Brix) and concentrated (pH 3.5 and 42 °Brix) orange juice was evaluated. A response surface methodology was employed to model the combined effects of factors on the enzyme inactivation. The main effects were described by linear or quadratic functions. For both single strength and concentrated orange juices, the effects of all three main factors and some interactions (pressure level, cycle and holding time) were statistically significant (p<0.05). The dual nature of pressure inactivation of PME (with an instantaneous inactivation due to a pressure pulse, instantaneous pressure fall, and first order rate of inactivation during the pressure hold, yielding D and z values) reported in earlier studies was confirmed. Combination models were developed to predict the residual enzyme activity as influenced by the pressure level, number of pressure cycles and pressure hold time. [source]

Surface Modification with Pressure Pulse Plasmas

PLASMA PROCESSES AND POLYMERS, Issue 6-7 2009
Andreas Holländer
Abstract In plasma treatments, the process gas is usually fed into the chamber in a more or less continuous way. The pulsing of the process gas can provide new opportunities. Some of them are explored in this paper. The interrupted or alternating process gas flux can help in mixing the sample in an activation treatment of a polyethylene powder. If the pores are not too small, a pressure pulse can help to improve the oxidation inside a porous polyolefin material. A plasma polymerization of ethene or allylamine can be more efficient if the timing of a plasma power pulse and the monomer pulse is optimized. Radicals are formed in the surface during the plasma pulse and these radicals initiate a polymerization of the monomer at a higher pressure. [source]

An example of a test method for vent sizing,OPPSD/SPI methodology

PROCESS SAFETY PROGRESS, Issue 2 2002
Charles S. Poteet III
An alternative methodology to that of United Nations, Appendix 5, Sample Method, has been developed by the Organic Peroxides Producers Safety Division of the Society of the Plastics Industry (OPPSD/SPI) to assure the safe emergency venting of organic peroxides in an approved container. The methodology is applicable for designing a new container for an existing or new organic peroxide. Bench-scale testing with a 10 liter vessel determined the maximum pressure pulse (spike) generated during a thermal decomposition/overpressurization vs. the ultimate, structural strength of the container measured and/or calculated. The methodology has been tested full scale with a United Nations 6(c) fuel fire. Container deformation, so long as there is no fragmentation, is permitted with the proviso that the container be retired from service following an incident. The methodology, as developed, reflects advances in technology while "harmonizing" to a maximum extent with the United Nations, Appendix 5, Sample Method. [source]

Inner ear pressure changes in normal guinea pigs induced by the Meniett 20

CLINICAL OTOLARYNGOLOGY, Issue 4 2001
R.A. Feijen
Introduction. The objective was measurement of inner ear fluid pressure changes of normal guinea pigs induced by the Meniett 20 (Pascal Medical, Sweden), a possible therapeutic pressure generator to be used by patients with Menière's disease. Methods. In seven guinea pigs, the tip of a micropipette was inserted into the inner ear via the round window membrane, reached by a retroauricular approach. A small hole was cut in the tympanic membrane and the bulla was closed again. Middle ear pressure was altered via the external meatus using a pressure generator (Meniett 20) which produced complex oscillatory pressure pulses. Inner ear pressure was simultaneously measured with a WPI micropressure system. Results. Middle ear pressure changes were transferred instantly to the inner ear of guinea pigs. Inner ear pressure declined while middle ear pressure kept relatively stable. An average undershoot of ,1.0 cm water with respect to the steady state pressure was seen after application of a pressure pulse, which was released in a few seconds. There was no change in steady state inner ear pressure after a complete session. Conclusion. Complex oscillatory pressure pulses produced by the Meniett 20 applied to the middle ear of guinea pigs causes a transient reduction of inner ear fluid volume. [source]

Respiratory units of motor production and song imitation in the zebra finch

Near-lithostatic pore pressure at seismogenic depths: a thermoporoelastic model

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006
Francesca Zencher
SUMMARY A model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure. This configuration is thought to be pertinent to the South Iceland seismic zone (SISZ) and to other tectonically active regions of recent volcanism, where volatiles are continuously released by ascending magma below the brittle,ductile transition. Poroelastic parameters are computed for basaltic rock. The model is 1-D, the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium. Environment conditions are considered, pertinent to basalt saturated with water at shallow depth (case I) and at mid-crustal depth (case II). If the intrinsic permeability of the rock is high, no significant effects are observed in the pressure field but advective heat transfer shifts the brittle,ductile transition to shallower depths. If the intrinsic permeability is low, the pressure-dependent permeability can propagate near-lithostatic pore pressures throughout most of the transition layer, while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition. Geometrical parameters characterizing the fracture distribution are important in determining the effective permeability: in particular, if an interconnected system of fractures develops within the transition layer, the effective permeability may increase by several orders of magnitude and near-lithostatic pore pressure propagates upwards. These modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the SISZ, in connection with the two 2000 June M= 6.5 earthquakes, including: (i) fluid pressure pulses in deep wells, (ii) low resistivity at the base of the seismogenic layer, (iii) low VP/VS ratio and time-dependent seismic tomography, (iv) heterogeneity of focal mechanisms, (v) shear wave splitting, (vi) high b -value of deep foreshocks, (vii) triggered seismicity and (viii) Radon anomalies. [source]

Ventricular Fibrillation Induced by Stretch Pulse: Implications for Sudden Death Due to Commotio Cordis

Lactobacillus reuteri ingestion and IKCa channel blockade have similar effects on rat colon motility and myenteric neurones

NEUROGASTROENTEROLOGY & MOTILITY, Issue 1 2010
B. Wang
Abstract, Background, We have previously shown that ingestion of Lactobacillus reuteri may modulate colonic enteric neuron activity but with unknown effects on colon motility. The aim of the present report was to elucidate the neuronal mechanisms of action of the probiotic by comparing the effects on motility of L. reuteri ingestion with blockade of a specific ionic current in enteric neurons. Methods, We have used intraluminal pressure recordings from ex vivo rat colon segments and whole cell patch clamp recordings from neurons of rat longitudinal muscle myenteric plexus preparations to investigate the effects of L. reuteri and TRAM-34 on colon motility and neurophysiology. The effects of daily feeding of 109L. reuteri bacteria or acute application of TRAM-34 on threshold fluid filling pressure or pulse pressure was measured. Key Results,Lactobacillus reuteri increased intraluminal fluid filling pressure thresholds for evoking pressure pulses by 51% from 0.47 ± 0.17 hPa; the probiotic also decreased the pulse pressure amplitudes, but not frequency, by 18% from 3.91 ± 0.52 hPa. The intermediate conductance calcium-dependent potassium (IKCa) channel blocker TRAM-34 (3 ,mol L,1) increased filling threshold pressure by 43% from 0.52 ± 0.22 hPa and reduced pulse pressure amplitude by 40% from 2.63 ± 1.11 hPa; contraction frequency was unaltered. TRAM-34 (3 ,mol L,1) reduced membrane polarization, leak conductance and the slow afterhyperpolarization current in 16/16 myenteric rat colon AH cells but 19/19 S cells were unaffected. Conclusions & Inferences, The present results are consistent with L. reuteri enhancing tonic inhibition of colon contractile activity by acting via the IKCa channel current in AH cells. [source]

Coronary Blood Flow Produced by Muscle Contractions Induced by Intracardiac Electrical CPR during Ventricular Fibrillation

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 2009
HAO WANG M.D.
It has been reported that transthoracic electrical cardiopulmonary resuscitation (ECPR) generates coronary perfusion pressures (CPP) similar to manual chest compressions (MCC). We hypothesized that intracardiac ECPR produces similar CPP. Methods: ECPR pulse train protocols were applied for 20 seconds in a porcine model following 10 seconds of ventricular fibrillation (VF), using a defibrillator housing electrode and a right ventricular coil (IC-ECPR). Each protocol consisted of 200-ms electrical pulse trains applied at a rate of 100 pulse trains/min. The protocols were grouped in skeletal-based versus cardiac-based stimulation measurements. CPP was recorded and compared to historical MCC values generated by a similar experimental design. CPP > 15 mm Hg at 30 seconds of VF following the application of an IC-ECPR protocol was defined as successful. Results: Mean CPP for all intracardiac ECPR pulse train protocols at 30 seconds of VF was 14.8 ± 3.8 mm Hg (n = 39). Mean CPP in seven successful skeletal-based IC-ECPR protocols was 19.4 ± 3.2 mm Hg, and mean CPP in 10 successful cardiac-based IC-ECPR protocols was 17.4 ± 2.1 mm Hg. Reported CPP for 15 MCC experiments at 30 seconds of VF was 22.9 ± 9.4 mm Hg (P = 0.35 compared to skeletal-based IC-ECPR, P = 0.08 compared to cardiac-based IC-ECPR). Conclusions: Intracardiac applied electrical CPR produced observable skeletal muscle contractions, measurable pressure pulses, and coronary perfusion pressures similar to MCC during a brief episode of untreated VF. [source]